The present invention relates to a developer composition and more particularly to a developer composition suitable for removing from presensitized plates areas which are to be non-image portions of negative working and/or positive working lithographic printing plates.
Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J.P. KOKOKU") No. 56-39464 discloses a developer composition for removing un-exposed areas of a light-sensitive layer composed of a weak alkaline water-soluble organic polymer and a light-sensitive diazo resin. However, this developer composition does not show satisfactory ability of completely removing un-exposed portions of a light-sensitive layer adjacent to the surface of a substrate. For this reason, when the composition is used as a developer for a presensitized plate for making a lithographic printing plate (hereunder referred to as "PS plates"), background contamination is caused during printing operations. It has been known that such a disadvantage can be eliminated by adding a sulfite as disclosed in J.P. KOKOKU No. 56-42860 to the foregoing developer composition. Thus, the addition of such a reducing inorganic sulfite makes it possible to solve the problem of background contamination of the non-image areas during printing, but if the developer is stored for a long time period, a part of the sulfite is oxidized and thus the effect of preventing background contamination is impaired. On the other hand, as the developer in which hard water is used deteriorates, binders are precipitated out from the developer to form sludge. However, if a chelating agent (softening agent for hard water) is added thereto to prevent the formation of such sludge, the oxidation of sulfite is accelerated and in turn the deterioration of the developer is promoted.
PS plates having a positive working light-sensitive layer have also widely been used, like the negative working PS plates. However, a developer for such positive working PS plates generally differs from that for the negative working ones. Therefore, a plurality of developer compositions and a plurality of processing apparatuses are required for processing these two kinds of PS plates. This is economically unfavorable. Moreover, wide space is required for installing the apparatuses and thus workability is impaired.